This disclosure pertains to microlithography (transfer of a pattern to a sensitive substrate), especially as performed using a charged particle beam. Microlithography is a key technology used in the fabrication of microelectronic devices such as integrated circuits, displays, and micromachines. More specifically, the disclosure pertains to monitoring the respective temperature of various components of a microlithography apparatus (e.g., lenses, deflectors, and stages), and taking corrective action when a temperature anomaly is detected.
In recent years, the resolution limitations of optical microlithography (specifically, microlithography performed using a beam of ultraviolet light) have become increasingly apparent. Hence, substantial development effort currently is being expended to develop a practical xe2x80x9cnext-generationxe2x80x9d microlithography technology. A principal candidate next-generation microlithography technology is so-called high-throughput, reduced-projection charged-particle-beam (CPB) microlithography. CPB microlithography offers prospects of much finer resolution than optical microlithography for reasons similar to the reasons for which electron microscopy yields better imaging resolution than optical microscopy. In fact, CPB microlithography apparatus currently under development have exhibited an ability to resolve substantially smaller linewidths and feature sizes than obtainable using optical microlithography.
CPB microlithography apparatus (employing, as a charged particle beam, an electron beam or ion beam) comprise CPB lenses, deflectors, and stigmators that include electromagnetic coils and the like. It has been found that the operating characteristics of an electromagnetic coil change if the coil experiences a temperature change (e.g., heat generated by passage of electrical current through the coil or heat conducted to the coil from an extraneous source). Such changes in the operating characteristics adversely affect the imaging characteristics and image-position control aspects of the CPB optical system of which the affected lens or coil is a part. As the demands of achieving ever-finer pattern resolution become more pressing, the need to provide temperature control of these components becomes an increasingly serious problem in CPB microlithography apparatus.
Various temperature-control devices and mechanisms are known. However, conventional devices and mechanisms have limited responsiveness and controllability that simply are inadequate for the demands of modern CPB microlithography. Consequently, using conventional temperature-control devices, it has been impossible from a practical standpoint to achieve the requisite constantly controlled temperatures with high accuracy and precision. It also has been impossible to eliminate component deformation due to temperature fluctuations.
In view of the shortcomings of conventional technology summarized above, the invention provides, inter alia, CPB microlithography apparatus and methods that are more thermally stable and hence achieve more accurate and stable exposures.
To such end, a first aspect of the invention is directed, in the context of microlithography apparatus for transferring a pattern onto a sensitive substrate using a charged particle beam, temperature-control devices. An embodiment of a temperature-control device is associated with components of a CPB optical system as used for imaging the pattern at specified locations on the substrate. The embodiment includes a respective temperature sensor associated with at least one component of the CPB optical system. The embodiment also includes a temperature-monitoring device to which the at least one temperature sensor is connected. The temperature-monitoring device is configured to receive the respective temperature-detection signals from the at least one temperature sensor, to ascertain whether the temperature-detection signals indicate existence of a temperature anomaly, and to produce respective temperature-control commands. The device also includes a controller to which the temperature-monitoring device is connected. The controller is configured to receive the temperature-control commands from the temperature-monitoring device and, if the temperature-control commands indicate existence of the temperature anomaly, to initiate at least one action selected from triggering an alarm, stopping exposure, and calibration of the microlithography system. With such a device, changes in temperature of respective component(s) are detected and monitored, wherein the CPB microlithography apparatus is controlled according to the respective magnitudes of the changes. In any event, temperature changes of the component(s) are more rapidly dealt with than conventionally, allowing a more stable exposure to be achieved.
The CPB optical system typically comprises a CPB source, at least one condenser lens, at least one projection lens, at least one deflector, and at least one stage. In such a configuration, a respective temperature sensor desirably is associated with each of the CPB source, the at least one condenser lens, the at least one projection lens, the at least one deflector, and the at least one stage.
The temperature-control device can further comprise a display connected to the temperature-monitoring device and configured to display temperature data as obtained by the at least one temperature sensor and interpreted by the temperature-monitoring device.
The temperature-control device can further comprise a warning device connected to the temperature-monitoring device and configured to activate an alarm if a temperature detected by a temperature sensor exceeds a respective specification, thereby indicating existence of the temperature anomaly.
The temperature-monitoring device can be configured to ascertain whether the temperature-detection signals indicate a temperature anomaly in which a temperature as sensed by a temperature sensor has exceeded a specified value or has exceeded a specified xe2x80x9cgradientxe2x80x9d (i.e., rate of change, especially from lower to higher temperature). The specified value or gradient varies with different CPB optical systems and/or different CPB microlithography systems. By way of example, the temperature-monitoring device can be configured to trigger the alarm whenever a detected temperature gradient is at least 0.04xc2x0 C./s, to trigger a calibration of the CPB microlithography apparatus whenever a detected temperature gradient is at least 0.08xc2x0 C./s, and to trigger a halt of exposure whenever a detected temperature gradient is at least 0.1xc2x0 C./s.
According to another aspect of the invention, microlithography methods are provided for transferring a pattern onto a sensitive substrate using a charged particle beam passing through a CPB optical system. According to an embodiment of such a method, respective temperatures of components of the CPB optical system are detected. The respective detected temperatures of the components are continuously monitored so as to produce temperature-monitoring data. The temperature-monitoring data are processed, including comparing the data to respective specified temperature data for the respective components to determine whether the temperature-monitoring data indicate existence of a respective temperature anomaly. If a temperature anomaly is indicated, then at least one action is triggered, selected from triggering an alarm, stopping exposure, and calibration of the microlithography system.
This method embodiment can further include the step of displaying the temperature-monitoring data, which desirably are displayed in real time. Thus, an operator can easily check the temperature status of the microlithography system and rapidly respond to sudden temperature changes, for example, of any of the monitored components.
The CPB optical system can comprise a CPB source, at least one condenser lens, at least one projection lens, at least one deflector, and at least one stage. In this context, the detecting step can comprise detecting a respective temperature of each of the CPB source, the at least one condenser lens, the at least one projection lens, the at least one deflector, and the at least one stage.
The monitoring step can include ascertaining whether a detected temperature has exceeded a specified value or has exceeded a specified gradient indicative of the temperature anomaly. For example, the action-initiating step can comprise: triggering an alarm whenever a detected temperature gradient is at least 0.04xc2x0 C./s, triggering a system calibration whenever a detected temperature gradient is at least 0.08xc2x0 C./s, and triggering a halt of exposure whenever a detected temperature gradient is at least 0.1xc2x0 C./s.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.